"hai mươi lăm" is the standard way to say the number. Northerners often say "hai mươi nhăm" as in some Northern provinces, people cannot pronounce the sound /l/

you should say " hai mươi năm" only the sound is different

Standard speaking doesn't matter,... as long as u know the original Vietnamese accent ... they will always understand u

Ho chi minh City: hai mươi lăm ( Saigonese accent) Other accent: hai mươi nhăm, hai mươi lem,hai mươi nhem,...

"Hai mươi lăm" is standard way and seems to be more modern way. "Hai mươi nhăm" is popularly spoken in the North of Vietnam in the past. Now it is used mostly by aged people whose origin is in the North.